This applications claims the priority of Japanese Patent Nos. 2000-025854, 2000-048721, 2000-075226, 2000-110418, 2000-134611, 2000-234227, 2000-255876, the contents of all of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method for forming a magnetic pattern in a is magnetic recording medium used for a magnetic recording device, a magnetic recording medium, or a magnetic recording device. In particular, the present invention relates to a method for forming a magnetic pattern in a magnetic recording medium, a magnetic recording medium, or a magnetic recording device wherein the magnetic recording medium has a magnetic layer, a protective layer, and a lubricant layer, where a flying/contact magnetic head used for recording or reproducing.
2. Background of the Invention
Magnetic recording devices such as a magnetic disk device (a hard disk drive) have widely been used as external memory devices for information processing devices such as computers, and have recently been used as recording devices for devices for recording dynamic images or set-top boxes.
A typical magnetic disk device includes a shaft for holding a single or plurality of magnetic disks while penetrating the center of the magnetic disk or disks, a motor for rotating the magnetic disk or disks that is or are connected to the shaft by interposing a bearing or bearings, a magnetic head for recording/reproduction information, an arm for supporting the magnetic head, and an actuator for moving the magnetic head via the arm to a desired position on the magnetic recording medium. As the recording/reproduction head, a flying magnetic head capable of moving above the magnetic recording medium at a constant flight height is generally used.
In addition to a flying magnetic head, a contact magnetic head is proposed in order to reduce the distance from the magnetic head to the medium. The magnetic recording medium to be placed in the magnetic disk device is prepared, in general, by forming a NiP layer on the surface of a substrate that includes an aluminum alloy, applying a smoothening treatment, a texturing treatment, or the like thereon, and then forming a metallic underlayer, a magnetic layer (an information recording layer), a protective layer, a lubricant layer, and the like in this order thereon. Or, the magnetic recording medium is prepared by forming a metallic underlayer, a magnetic layer (an information recording layer), a protective layer, a lubricant layer, and the like on the surface of a substrate made of glass or the like. The magnetic recording medium includes a longitudinal magnetic recording medium and a perpendicular magnetic recording medium. In the longitudinal magnetic recording medium, longitudinal recording is generally conducted.
The rate of increase in the density of magnetic recording media is increased year by year, and various techniques for increasing density have been proposed. For example, there are attempts to make the flying height of the magnetic head smaller, to employ a GMR head as the magnetic head, to improve a magnetic material used for the recording layer of the magnetic disk so as to have a strong coercive force, and to reduce the space between tracks for recording information in the magnetic disk. For example, a density of track of 100 ktpi or more is needed in order to realize 100 Gbit/inch2.
In each track, a magnetic pattern for controlling the magnetic head is formed. For example, it produces signals used for controlling the position of the magnetic head or signals used for synchronous control. When the space between adjacent information recording tracks is narrowed to increase the number of tracks, it is necessary to increase the density of the signals for controlling the position of a data-recording/reproduction head (hereinbelow, referred to as xe2x80x9ca servo signalxe2x80x9d) in the radial direction of the disk. In other words, in response to the increased number of tracks, an increased number of signals for controlling the position of a data-recording/reproduction head much is required so that precision control can be performed.
Further, there is an increased demand for increases in the width of the data recording area. This would allow an increase in the data recording capacity by reducing the surface area not used for recording data, namely, the servo areas used for recording servo signals and the gap portions between the servo areas and the data recording areas. Thus, it is necessary to increase the data content of the servo signals or to increase the accuracy of synchronizing signals.
In a conventional method that is used widely in manufacturing, an opening is formed in the vicinity of the head actuator of the drive (magnetic recording device) and a pin with an encoder is inserted into the opening to engage the actuator with the pin. Servo signals are then recorded by moving the head to a correct position. However, methods based upon this approach encountered difficulty in correctly recording the servo signals because the position of the center of gravity of the actuator was different from the position of the center of gravity of a positioning mechanism, so that highly accurate track position control could not be obtained.
On the other hand, it has been proposed that laser beams be irradiated onto a magnetic disk to locally deform the surface of the disk. Minute projections and recesses can thus be physically formed and servo signals recorded by the minute projections and recesses. In this technique, however, there are problems such as the fact that: the projections and recesses make the flying magnetic head unstable and adversely influence the recording and/or reproduction of information; costly high power lasers are necessary for forming the projections and recesses; and relatively large amounts of time were required to successively form the individual projections and recesses.
In view of the above, several servo signal forming methods have been proposed.
For example, in one method a servo pattern is formed in a master disk having a magnetic layer with a high coercive force. The master disk is brought into close contact with a magnetic recording medium and then an external auxiliary magnetic field is applied to the magnetic recording medium, thus printing a magnetic pattern, as described in U.S. Pat. No. 5,991,104.
In another exemplary method, a medium that has previously been magnetized along a certain direction is formed. First, a ferromagnetic layer that includes a soft magnetic layer is formed by patterning on a master disk, and the master disk is brought into close contact with the medium. Then, an external magnetic field is applied. The soft magnetic layer functions as a shield, and a magnetic pattern is printed to an unshielded area, as described in Japanese Patent JP-A-50-60212, U.S. Pat. No. 3,869,711, Japanese Patent JP-A-10-40544, EP915456, and the article xe2x80x9cReadback Properties of Novel Magnetic Contact Duplication Signals with High Recording Density FDxe2x80x9d authored by R. Sugita et al., and published by IEEE in the Digest of InterMag 2000, GP-06 on Apr. 9, 2000.
With respect to forming a shield or using a magnetic recording source, the above-mentioned techniques use a master disk, and a magnetic pattern is formed in the medium by applying a strong magnetic field.
The intensity of a magnetic field generally is a function of distance. When a magnetic pattern is recorded by applying a magnetic field, the transitions in the magnetic pattern are apt to be blurred due to a leakage of the magnetic field. Accordingly, it is necessary to bring the master disk into intimate contact with the medium in order to minimize the influence of the leakage of the magnetic field. As the magnetic pattern becomes finer, it is necessary to intimately contact the master disk to the medium without any gap. Usually, both members are press-contacted using vacuum suction.
Further, the higher that the coercive force of the medium is, the larger the magnetic field required for transfer and, accordingly, the leakage of the magnetic field increases. Therefore, nearly perfect contact is required.
The above-mentioned techniques are applicable to a magnetic disk having a low coercive force or a flexible floppy disk that is easy to press contact. However, it is very difficult to use a magnetic disk for high density recording that includes a hard substrate where the coercive force is 3,000 Oe or more using these techniques.
Namely, with a magnetic disk that includes a hard substrate, there is the possibility that fine dust will deposit thereon before or during contact, causing a defect in the medium or even damaging the expensive master disk. In the particular case of a glass substrate, the deposition of dust may cause insufficiently close contact and it may become impossible to conduct magnetic printing. In some case, the magnetic recording medium cracked.
Further, in the technique described in Japanese Patent JP-A-50-60212 and U.S. Pat. No. 3,869,711, patterns at an angle oblique to the direction of tracks in a disk possessed only weak signal intensities, although recording was still possible. For a magnetic recording medium having a relatively high coercive force of 2,000-2,500 Oe or more, it is essential that a ferromagnetic material (as a shielding material) for forming a pattern in the master disk (such as permalloy or a soft magnetic material having a large saturation magnetic flux density such as sendust) be used in order to assure a sufficient magnetic field intensity for printing.
However, in the case of oblique patterns, a magnetic field formed by reversing the magnetization was oriented in a direction perpendicular to the gap produced by the ferromagnetic layer of the master disk, and it was impossible to incline the magnetization in a desired direction. As a result, a part of the magnetic field escapes into the ferromagnetic layer and a sufficient magnetic field could not be applied to a desired position during magnetic printing. Thus, a sufficient pattern of reversed magnetization could not be obtained, and it was difficult to produce high intensity signals. The reduction of a reproduced output using the oblique magnetic pattern was larger than the reduction by an azimuth loss, in comparison with a magnetic pattern perpendicular to the tracks.
Accordingly, it is one object of the present invention to provide a method of forming a magnetic pattern capable of efficiently and accurately forming various fine magnetic patterns without damaging the medium or the mask and without increasing defects in the medium.
It is another object of the present invention to provide a magnetic recording medium and a magnetic recording device that are capable of high density recording and can be produced in a short time in an economical manner.
The inventors of this application have studied extensively on the problems described above and have achieved the present invention by recognizing that a magnetic pattern can be effectively and accurately formed in a magnetic recording medium by combining local heating of the magnetic layer and with the application of an external magnetic field to the magnetic layer.
In accordance with a first aspect of the present invention, a method for forming a magnetic pattern in a magnetic recording medium having a magnetic layer, a protective layer, and a lubricant layer formed, in this order, on a substrate is described. This method is characterized by including local heating the magnetic layer and the application of an external magnetic field to the magnetic layer.
According to a second aspect of the present invention, a magnetic recording medium with a magnetic pattern is described. This magnetic pattern can be formed by the method for forming a magnetic pattern described in the first aspect of the present invention.
According to a third aspect of the present invention, a magnetic recording device is described. This magnetic recording device includes a magnetic recording medium in which a magnetic pattern is formed by the method of forming a magnetic pattern described in the first aspect, a driver configured to drive the magnetic recording medium in a recording direction, a magnetic head that includes a recording portion and a reproducing portion, a motion mechanism configured to move the magnetic head relative to the magnetic recording medium, and a recording/reproduction signal processor that supplies a recording signal to the magnetic head and receives a reproducing signal from the magnetic head.
According to a fourth aspect of the present invention, a magnetic pattern forming device is described. In this magnetic pattern forming device, a magnetic pattern is formed in a magnetic recording medium including a magnetic layer on a substrate by irradiating energy beams onto the magnetic recording medium to locally heat the magnetic layer and applying an external magnetic field to the magnetic layer. The magnetic pattern forming device is characterized in that it includes a medium support configured to hold the magnetic recording medium, an external magnetic field source configured to apply the external magnetic field to the magnetic recording medium, an energy beam source configured to emit energy beams, an energy beam irradiation device configured to direct the energy beams emitted from the energy beam source toward the magnetic recording medium, and a mask which is located between the energy beam source and the magnetic recording medium to change the spatial intensity distribution of the energy beam in order to form a desired magnetic pattern.
According to a fifth aspect of the present invention, a method for producing a magnetic recording medium is described. This magnetic recording medium includes a magnetic layer, a protective layer, and a lubricant layer formed on a substrate in this order. A magnetic pattern is formed in the magnetic layer, and the method is characterized in that it includes a step of forming the magnetic layer and the protective layer on the substrate, a step of forming the lubricant layer on the protective layer, and a step of forming the magnetic pattern by local heating of the magnetic layer together with the application of an external magnetic field.